Failsafe system for electrostatic copying apparatus

ABSTRACT

An electrostatic copying apparatus wherein a photoelectric detector scans the path for transfer sheets which receive powder images from a drum-shaped xerographic surface. The detector cooperates with two timers the first of which is actuated by the latent image producing device to furnish signals at intervals when the detector normally should not detect sheets and the second of which is also actuated by the latent image producing device but at such intervals that it furnishes signals when the detector normally should detect transfer sheets. The operation of the apparatus is terminated if a signal from the detector coincides with the signal from the first timer because this indicates a pileup of sheets, and also if a signal from the detector does not coincide with a signal from the second timer because this indicates the exhaustion of the supply of sheets in the apparatus. The detector scans the path for the sheets upstream of a fusing station wherein the powder images are fixed to respective sheets.

United States Patent 1 1 Szostak et a1. 45 May 22, 1973 541 FAILSAFE SYSTEM FOR 3,150,873 9/1964 MacGregor ..340/259 x ELECTROSTATIC COPYING 3,650,616 3/1972 Hudson APPARATUS 3,626,956 12/1971 Sauder ..271/57 X [75] Inventors: ii fg ggggw a gx: Primary Examiner-Richard L. Moses Mauris llat, Munich, all if Germany Att0mey Mlchael Striker [73] Assignee: Afga-Gevaert Aktiengesellschaft, [57] ABSTRACT Leverkusen Germany An electrostatic copying apparatus wherein a [22] Filed: Sept. 17, 1971 photoelectric detector scans the path for transfer sheets which receive powder images from a drum- [21] Appl' 18l374 shaped xerographic surface. The detector cooperates with two timers the first of which is actuated by the 1 1 Foreign Application Priority Data latent image producing device to furnish signals at in- Sept. 22, 1970 Germany ..P 20 46 681.3 tervals the detector many shuld detect sheets and the second of which is also actuated by the 52 11.5. C1. ..355/14, 271/57, 340/259, latent image Producing device but at Such intervals 55 that it furnishes signals when the detector normally [51] Int. Cl. ..G03g 15/00 Should detect transfer Sheets- The operation of the P [58] Field of Search ..355 14, 3, 8; paratus is terminated if a Signal from the detector 271/57; 340/259 coincides with the signal from the first timer because this indicates a pileup of sheets, and also if a signal [56] References Cited from the detector does not coincide with a signal from the second timer because this indicates the exhaustion UNITED STATES PATENTS of the supply of sheets in the apparatus. The detector 3,439,983 4/1969 Blow ..355/8 Scans the P for the Sheets upstream of a fusing 3,588,472 6/1971 Glaster... ..355/14 X tion wherein the powder images are fixed to respective 3,586,450 6/1971 Hosey ..355/14 X sheets. 3,635,555 l/l972 Kurahashi et a1 ..355/8 3,453,500 7/1969 Lundin et a1. ..340/259 X 12 Claims, 2 Drawing Figures PATENTED nmzzlsn SHEET 1 [IF 2 IN VEN TOR R0 LAND SZOSTAK KARL HAR BY GUNTER MAURISCHAT *imlaa /L-[p 1 FAILSAFE SYSTEM FOR ELECTROSTATIC COPYING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to improvements in electrostatic copying apparatus of the type wherein successive strip-shaped portions of originals are imaged onto a xerographic surface which is in continuous motion and moves at the exact speed of the original as well as at the exact speed of sheet-like transfer material which is to receive a powder image from the xerographic surface. The freshly transferred powder image is thereupon caused to pass through a fusing station to insure that it is permanently affixed to transfer material.

A drawback of the presently known electrostatic copying apparatus of the just outlined character is that the sheets of transfer material, which normally consist of paper, are likely to pile up in front of or at the fusing station and to be heated to kindling temperature whereby the entire apparatus can go up in flames. Such damage to or complete destruction of the copying apparatus is likely to occur if the feeder for sheets of transfer material continues to operate after a sheet has been caught in the apparatus in close or immediate proximity of heated parts at the fusing station.

SUMMARY OF THE INVENTION y struction of the apparatus.

Another object of the invention is to provide the copying apparatus with an additional safety device which insures automatic stoppage of the apparatus (or at least all important component parts of the apparatus) in response to exhaustion of the supply of sheets of transfer material.

A further object of the invention is to provide the electrostatic copying apparatus with a novel electric circuit which embodies the just discussed safety devices.

An additional object of the invention is to provide the copying apparatus with a single detector for sheets of transfer material which can be used to initiate the operation of either safety device.

Still another object of the invention is to provide an electrostatic copying apparatus which can be utilized to furnish any desired number of copies of a single original and wherein such versatility of the apparatus can be achieved by a device which performs at least one additional important function.

The invention is embodied in an electrostatic copying apparatus having a driven xerographic surface which is preferably a cylindrical surface and is moved at a predetermined speed, means for producing on the xerographic surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of such surface, means for converting the latent images into powder images, for example, by spraying the latent images with a suitably colored toner, feeding means for transferring successive powder images onto successive sheets of transfer material (which are normally separated from each other by gaps each extending the trailing edge of-a preceding sheet and the leading edge of the next-following sheet) by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts the xerographic surface at a first point and moves out of contact with such surface at a second point, fusing means adjacent to the path downstream of the second point and having means for fixing the powder images to respective sheets (preferably by heating the toner to melting temperature but below the kindling temperature of the sheets), sheet advancing means adjacent to the path downstream of the fusing means, photoelectric detector means adjacent to a predetermined portion of the path intermediate the second point and the advancing means (preferably between the second point and the fusing means) and serving to produce signals in response to detection of sheets in the predetermined portion of the path, and signal generating timer means which is actuable (preferably by the means for producing latent images on the xerographic surface) at such intervals that, while the timer means is being actuated, the detector means does not produce a signal because the actuation of the timer means should take place whenever a gap is located in the predetermined portion of the path in the course of normal transport of sheets along the path and into the range of the advancing means so that the detector means then normally fails to detect sheets in the predetermined portion of the path. Simultaneously generation of signals by the detector means and by the timer means indicates the likelihood of a pileup of sheets, and such simultaneous signals are used to bring about at least partial stoppage of the copying apparatus.

The stoppage of the apparatus may involve turning off or arresting all movable parts, such as the xerographic surface, the components of the latent image forming means, the component or components of the converting means, the component or components of the feeding means, and the heating device of the fusing means.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved copying apparatus it-, self, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific; embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING I I FIG. 1 is a schematic representation, in partial section, of a presently preferred embodiment of the copying apparatus; and

FIG. 2 is a circuit diagram of the apparatus shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS opment apparatus, which comprises a drum-shaped xerographic surface 1 (hereinafter called drum) which is connected with the ground by way of its drive shaft l'a.

The periphery of the drum 1 is provided with the customary photoconductive layer of selenium successive increments of which travel along a charging station 101 accommodating a corona discharge device 2. The shaft 1a receives torque from a main prime mover 58 (FIG. 2) and drives the drum 1 in a counterclockwise direction as indicated by the arrow A so that the increments on which a uniform electrostatic charge is deposited by the corona discharge device 2 move past an exposure station 102 accommodating the objective lens 3 which images on the drum 1 successive strips of an original 4, e.g., a copy to be reproduced. The original 4 is illuminated by two tubular lamps 5, 6 and is supported by a carriage 7 which is reciprocable by a drive including a cord or cable and a helical resetting spring 21. The cord 8 moves the carriage 7 (and the original 4 thereon) forwardly (arrow B) at the exact peripheral speed of the drum 1. It will be noted that the direction of forward movement of the carriage 7 (arrow B) is counter to the direction of rotation of the drum 1 (arrow A). The forward end of the cord 8 is connected to a pulley (not shown) which is coupled to the drum 1 in response to energization of an electromagnetic clutch (not shown) which can be energized by a starter switch accessible to the operator of the copying apparatus. The circuit of the electromagnetic clutch is opened by the carriage 7 when the latter completes a forward stroke (arrow B) of predetermined length whereby the resetting spring 21 returns the carriage 7 to a starting position (to the left of the position shown in FIG. 1) in which the carriage abuts against a fixed stop 20. Such clutches are well known from the art of electrostatic copying apparatus. The parts 3, 5, 6, 7 and the drive for the carriage 7 together constitute a means for producing on the drum a series of electrostatic latent images by repeatedly im'aging successive portions of a single original 4 or by imaging successive portions of several discrete originals, one after the other.

The electrostatic latent images of one or more originals 4 are transported past a development station 103 accommodating a conventional dispenser 19 for pulverulent developing material of the type known as toner. The dispenser 19 constitutes a means for converting latent images into powder images which adhere to the drum 1. The toner is normally a pigmented resin which is held on the drum 1 electrostatically to form thereon a powder image pattern which is thereupon transferred onto a sheet-like transfer material a (hereinafter called sheets) at a transfer station 104. The sheets 10a normally consist of paper and are removed seriatim from a stack 10 on a table 10A by a feeder 9 having a roller 9d which engages the topmost sheet of the stack 10 while moving in a forward direction (arrow C). The feeder 9 is connected with a cable or cord 9a which can be driven by the drum 1 in the same way as the cord 8, i.e., by an electromagnetic clutch (not shown) which can drive a pulley or sheave attached to the forward end of the cord 9a. A helical resetting spring 911 returns the feeder 9 to a starting position, in which a projection of the feeder abuts against a stop 90, as soon as the clutch is deenergized so that the pulley for the cord 9a ceases to share the angular movement of the drum 1. The clutch for the pulley of the cord 9a is energized by a switch (not shown) which is actuated by the carriage 7 in such a way that the leading edge of a freshly withdrawn sheet 10a enters the transfer station 104 simultaneously with the powder image on the photoconductive layer of the drum 1. The

switch for the just discussed electromagnetic clutch is opened by the carriage 7 to deenergize the clutch and to permit return movement of the feeder 9 under the action of the resetting spring 9b when the leading edge of the freshly delivered sheet 10a contactsthe periphery of the drum 1. The carriage 7 can be provided with lobes, cams, arms or analogous actuating means for the switches which control the electromagnetic clutches for the cords 8 and 9a. The leading edge of .a freshly withdrawn sheet 10a enters the transfer station 104 to contact the drum 1 at a first point P1 of a predetermined path 110 and the trailing edge of such sheet leaves the transfer station 104 and thus moves out of contact with the drum 1 at a second point P2 of the path 110.

The transfer station 104 accommodates a second corona discharge device 11 which provides the rear side of the sheet 10a with an electrostatic charge corresponding to that of the drum 1. This causes the particles of the negatively charged toner to adhere to the adjacent surface of the sheet 10a to form thereon an image of the original 4. The electrostatically transferred powder image is thereupon permanently fixed to the sheet 10a at a fusing or fixing station 106 which is adjacent to the path 110 but is not adjacent to the peripheral surface of the drum 1. Prior to reaching the fusing station 106, successive increments of each sheet 10a pass through a separating station 105 which accommodates a corona discharge device 13. The purpose of the corona discharge device 13 is to neutralize the charge which is applied to the rear side of the sheet 10a by the corona discharge device 11 at the transfer station 104. The separating station 105 may further accommodate a blower nozzle 16 having one or more orifices 16a which discharge one or more streams of slightly compressed air to further promote the separation of successive sheets 10a from the drum 1.-The nozzle l6 constitutes a desirable but optional feature at the separating station 105; the source of compressed gas for this nozzle is not shown in FIG. 1. Such compressed gas can be furnished by the blower 61 (FIG. 2) of a cooling device for the copying apparatus, especially for the parts at the fusing station 106. The separating station 105 can be said to form the rightmost part of the transfer station 104 andis adjacent to that portion of the path which includes the point P The parts at the fusing station 106 include a heat radiating device 15 above and a metallic plate-like guide 18 below the path 110 for successive sheets 10a. The heat which is generated by the device 15 causes the particles of toner to melt and to be absorbed by the material of the respective sheets 10a. The fusing station 106 is located immediately upstream of two sheet advancing rolls 17a, 17b at least one of which is driven by the prime mover 58 or by the drum 1 to move the sheets 10a into an intercepting receptacle which is accessible from without the copying apparatus.

After moving beyond the separating station 105, successive increments of the drum 1 travel pasta cleaning station 107 which accommodates a rotary brush 14 serving to remove the remnants of toner before the thus cleaned increments of the photoconductive layer reenter the charging station 101.

In accordance with a feature of the present invention, the electrostatic copying apparatus further comprises a photoelectric detector PD including a light source 24 which emits a beam of light against the dark peripheral detector PD is adjacent to a shield 22 which insures that the'light-sensitive surface of the element 23 is exposed only or mainly to light which issues from the source 24 and is reflected on the drum 1 or on a passing sheet a.

As shown in FIG. 2, the light sensitive element 23 of the photoelectric detector PD is connected in series with a resistor 27 and by a conductor 25 to the negative pole of a source of 12 volt current. A second conductor 26 connects the resistor 27 with the positive pole of a source of 12 volt current. The resistance of the resistor 27 is much smaller then the resistance of the light sensitive element 23 when the latter receives light which is emitted by the light source 24 and is reflected on the dark peripheral surface of the drum 1. Thus, the potential at the junction 28 between the resistor 27 and the light sensitive element 23 is then a positive potential.

' need not be white, as long as their opacity is sufficiently less than the opacity of the peripheral surface on the drum 1 to thus insure that the resistance of the light sensitive element 23 is less than the resistance of the resistor 27 when the element 23 is exposed to light which is reflected on a sheet 10a. It will be noted that the just described components of the electric circuit which is shown in FIG. 2 act not unlike a switch which applies to the junction 28 a positive potential in the absence of a sheet 10a between the stations 105, 106 and a negative potential when the photoelectric detector PD detects a sheet 10a.

The junction 28 is connected with a conductor 29 which is connected with two differential amplifiers 32, 33 by way of conductors 30, 31. The output of the amplifier 32 is connected with one input of a first logical circuit here shown as an AND-gate 36 by a conductor 34, and the output of the amplifier 33 is connected with one input of a second logical circuit or AN D-gate 37 by a conductor 35. The other inputs of the AND-gates 36, 37 can be connected with the conductor 26 by conductors 38, 42 and 39, 43. The conductors 39, 43 are connected to the contacts of a first timer here shown as a microswitch 41, and the conductors 38, 42 are connected with the contacts of a second timer or microswitch 40. As shown in FIG. 1, the microswitches 40, 41 are respectively provided with trips 40a, 41a which can be displaced by a projection 142 of the carriage 7 for originals 4. The microswitch 41 is positioned in such a way that it is closed by the projection 142 in the very moment when the trailing edge of a sheet 10a has moved beyond the detector PD in the course of normal operation of the copying apparatus. The microswitch 41 can cause the output of the AND-gate 37 to transmit a signal in the event of a pileup of sheets 10a in the copying apparatus, namely, between the stations 105 and 106. j

The projection 142 of the carriage 7 causes the trip 40a to close the microswitch 40 at such intervals that when, if the copying apparatus operates normally, the light sensitive surface of the element 23 must be exposed to light which is reflected on a sheet 10a. Thus, the microswitch 40 can cause the output of the AND- gate 36 to transmit a signal which indicates the absence of sheets in the path 110 of the copying apparatus, and more particularly the absence of a sheet in the space between the stations and 106 at a time when the corresponding portion of the path for the sheets 10a should have accommodated a passing sheet.

The differential amplifier 32 is connected in the circuit of FIG. 2 in such a way that it transmits a signal via conductor 34 when the potential at the junction 28 is a positive potential, i.e., when the light sensitive element 23 of the detector is exposed to light which is re flected on the opaque surface of the drum 1. Since the microswitch 40 closes at a time when the portion of the path 110 between the stations 105 and 106 should accommodate a sheet 10a, the two inputs of the AND- gate 36 receive signals at the same time only when the operation is improper because a sheet 10a fails to advance toward the fusing station 106 at a time when the fusing station should receive a sheet. The differential amplifier 33 transmits to the corresponding input of the AND-gate 37 a signal when the potential at the junction 28 is a negative potential. Since the switch 41 closes at a time when the detector PD should not detect a sheet between the stations 105, 106 (and more particularly in that portion of the path 110 for sheets 10a which is traversed by the light beam issuing from the light source 24), the output of the AND-gate 37 will transmit a signal only when a sheet 10a has becomestuck in or ahead of thefusing station 106 or in the event of a pileup of two or more sheets between the stations 105 and 106. The microswitch 41 is held by the projection 142 of the carriage 7 in closed position for an interval of time which normally elapses between the movement of the trailing edge of a preceeding sheet 10a beyond the beam issuing from the light source 24 and the movement of .the leading edge of the next following sheet 10a into such light beam, i.e., while a gap between two successive sheets moves past the detector PD.

The outputs of the AND-gates 36, 37 are respectively connected with pulse transformers 47, 46. These trans: formers amplify the incoming signals and convert such signals into constant signals of proper polarity. The pulse transformer 46 is connected with a relay 49 by way of a conductor 48. The switch 55 of the relay 49 is connected in one power lead 56 of the main energy source for the current-consuming parts of the copying apparatus. Such current consuming parts include one or more lamps one of which is shown at 60, the main prime mover 58 which is an electric motor, the coils 59 Q of the radiation heater 15 at-the fusing station 106, and the aforementioned blower 61 of the means for cooling. the parts at the station 106.

The pulse transformer 47 is connected with a secondrelay 53 by way of conductors 50, 51 and a time-delay.- element 52. The switch 54 of the second relay 53 is also. connected in the power lead 56 of the main energy source which later further includes a second power lead 57. It will be noted that the opening of relay switch 54 results in stoppage of the motor 58 and in opening of the circuit of the lamp or lamps 60. The opening of switch 55 entails stoppage of the motor 58, opening of the circuit of the lamp or lamps 60, and opening of the circuit of the coil 59 in the readiation heater 15. The motor for the blower 61 is connected with the power leads 56, 57 in such a way that the blower 61 continues to cool the parts 15, 18 at the fusing station 106 even if the relays 49, 53 cause simultaneous opening of the switches 54 and 55. The operation of the copying apparatus is terminated in response to opening of the switch 54 or motor 58 which drives drum 1 (and hence the carriage 7 and feeder 9) as well as the wheel 19a of the dispenser 19, the brush 14, and the advancing rolls 17a, 17b.

THE OPERATION:

The switches 54, 55 are assumed to be closed so that the motor 58 drives the drum .1 (by way of the shaft la), the brush 14, the wheel 19a of the dispenser 19, and the advancing rolls 17a, 17b. The circuit of the coil 59 and lamp or lamps 60 is also completed and the blower 61 cools the parts 15, 18 at the fusing station 106. If the operator wishes to obtain a copy of an original 4 which has been placed onto the carriage 7, it is necessary to close a master switch (not shown) which energizes the electromagnet for the pulley of the cord 8 so that the carriage 7 begins to move in the direction indicated by the arrow B at the exact peripheral speed of the drum 1. The lens 3 images the original 4 on the drum 1 to form thereon an electrostatic latent image. As the carriage 7 moves in a direction to the right, as viewed in FIG. 1, it closes a switch (not shown) which energizes the electromagnet for the pulley of the cord 9a so that the feeder 9 begins to advance the topmost sheet 10a of the stack 10 in the direction indicated by the arrow C. When the carriage 7 has covered such a distance that, in the course of normal operation of the copying apparatus the leading edge of the freshly supplied sheet 100 would have to be located in front of the light source 24, the projection 142 closes the micros witch 40 by way of the trip 40a. The output of the AND-gate 36 transmits a signal to the pulse transformer 47 only if the detector PD detects the absence of a sheet 10a between the stations 105 and 106. The signal from the pulse transformer 47 is delayed by the element 52 which opens the switch 54 of the relay 53 after elapse of an interval which corresponds to that required for completion of a working cycle. The opening of switch 54 results in stoppage of the motor 58 and in opening of the circuit of the lamp or lamps 60. The circuit of the coil 59 in the radiation heater remains completed and the blower 61 continues to cool the parts 15, 18 at the fusing station 106. The operation of the copying apparatus can begin as soon as the supply of sheets 10a is replenished.

The microswitch 41 is open during the just described stage of operation so that the output of the AND-gate 37 cannot transmit a signal to the pulse transformer 46 and the switch 55 of the relay 49 remains closed. The trip 41a for the microswitch 41 is actuated by the projection 142 only when the trailing edge of a sheet 10a is supposed to have advanced beyond the light beam which is emitted by the light source 24 of the detector PD between the stations 105 and 106. If the detector detects the presence of a sheet 10a between such stations, the corresponding input of the AND-gate 37 receives a signal from the amplifier 33 and the pulse transformer 46 causes the relay 49 to immediately open the switch 55 and to this arrest the motor 58 simultaneously with opening of the circuit for the lamp or lamps 60 and coil 59. The blower 61 is not affected by the opening of switch 55 so that it can continue to cool those parts of the apparatus which are normally heated to an elevated temperature.

It will be noted that the photoelectric detector PD normally fails to produce such signals which cause immediate opening of the switch 55 and the resulting termination of operation of the copying apparatus. This is due to the fact that, in the course of normal operation, the light sensitive element 23 fails to produce signals simultaneously with those signals which are produced in response to closing of the timer or microswitch 41 because the microswitch 41 is closed at such intervals and for such periods of time that its closing coincides with the passage of a gap between two successive sheets 10a past that portion of the path which is scanned by the detector PD. However, if a sheet 10a happens to be located in the space between the stations 105, 106 at a time when this portion of the path 110 should not contain a sheet, the light sensitive element 23 causes the amplifier 33 to transmit a signal to the corresponding input of the AND-gate 37 at the exact moment when the other input of the AND-gate 37 receives a signal because the microswitch 41 is closed; the relay 49 is then energized without delay and immediately opens the switch 54 to terminate the operation of the copying apparatus.

On the other hand, the amplifier 32 transmits to the corresponding input of the AND-gate 36 a signal only when the light sensitive element 23 does not produce a signal which is indicative of the presence of a sheet 10a in that portion of the path 110 which extends between the stations 105, 106. Since the timer or microswitch 40 is closed at a time when, in the course of normal operation of the copying apparatus, the just mentioned portion of the path 110 should contain a sheet 10a, the signal from the output of the AND-gate 36 in dicates the absence of sheets 10a in the path 110, and such signals cause a stoppage of the apparatus (by way of the relay 53 and switch 54) with a delay which is determined by the element 52.

The just discussed timers 40, 41 for the logical circuits 36, 37 cooperate with the light sensitive element 23 of the photoelectric detector PD to insure automatic stoppage of the copying apparatus in response to a pileup of sheets 10a in that portion of the path 110 which extends between the advancing rolls 17a, 17b and the point P2 as well as in response to unwarranted absence of sheets 10a in such portion of the path 110. The pileup could cause heating of the arrested sheets to kindling temperature and the resulting fire could caused serious damage to or total destruction of the apparatus. The absence of sheets 10a can indicate the exhaustion of the supply of sheets 10a on the table 10A, and this warrants a stoppage of the apparatus. Furthermore, the operator can rely on the microswitch 40 to produce a desired number of copies of a single original 4. For example, an original can be placed onto the carriage 7 and a predetermined number of sheets 10a is then placed onto the table 10A. The copying apparatus is started and the microswitch 40 will cooperate with the light sensitive element 23 to automatically arrest the apparatus when the supply of sheets 10a on the table A is exhausted, i.e., when the apparatus has completed the making of a predetermined number of copies of a single original. This renders its unnecessary to equip the copying apparatus with a conventional selector knob which can be moved to several positions in each of which the apparatus produces a different number of copies of the same original, or the selector knob can be designed to serve as a means for preparing the apparatus for the making of one, two, three or four copies only.

Each of the switches 54, 55 can actuate a device which produces a visible or audible signal when the switch 54 or 55 opens. The lamp or lamps 60 can be said to constitute a device for generating visible signals (absence of illumination) in response to opening of the switch 54 or 55.

The operation of the light sensitive element 23 and microswitch 41 is in contrast to operation of safety devices in presently known electrostatic copying apparatus. As explained above, these parts will cooperate to cause the switch 55 to open without any delay if the portion of the path 110 which is scanned by the photoelectric detector PD does not accommodate a gap between a pair of successive sheets 10a at a time when the light beam issuing from the light source 24 should normally impinge on the dark surface of the drum 1. Such cooperation of the element 23 with the microswitch 41 is of advantage because the detector PD scans a portion of the path 1 10 wherein the accumulation of sheets 10a or unforeseen stoppage of a single sheet 10a could result in damage of the copying apparatus because the arrested sheet or sheets could be heated to kindling temperature. If the operator fails to immediately remove a single sheet which is stuck at the fusing station 106, the burning of such single sheet is not likely to cause serious damage to the copying apparatus. The nextfollowing sheets are unable to reach the fusing station 106 because the switch 55 opens in response to stoppage of a single or foremost sheet 10a in the space between the stations 105 and 106.

The microswitch 40 and the associated parts 36, 32, 47, 52, 53, 54 constitute a desirable optional feature of the copying apparatus. As explained above, these parts insure a delayed stoppage of the apparatus in response to detection of the absence of sheets 10a in a predetermined portion of the path 110 (between the advancing .rolls 17a, 17b and the point P2). Savings in space and material are achieved due to the fact that the photoelectric detector PD can cooperate with the microswitch 41 to indicate a pileup of sheets 10a as well as will the microswitch 40 to indicate the absence of sheets 10a. In each instance, the main prime mover 58 of the copying apparatus is arrested, either immediately or with a certain delay. As explained above, the provision of the microswitch 40 renders it possible to dispense with the customary knob which determines the number of copies to be made from a single original, or to simplify the controls for such selection by using a selector knob with a relatively small number of settings and by relying on the microswitch 40 to arrest the apparatus upon completion of a desired number of copies of a single original 4 (by placing a corresponding number of sheets 10a onto the table 10A and by allowing the apparatus to run until the supply of sheets on the table 10A is exhausted).

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can,

by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path; and timer means actuatable by said means for producing said latent images to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means.

2. A combination as defined in claim 1, further comprising drive means for continuously moving said sur face at a predetermined speed, said feeding means being arranged to convey said sheets into said path at said predetermined speed and said advancing means comprising a pair of rotary members located at the opposite sides of said path and means for rotating at least one of said rotary members.

3. A combination as defined in claim 1, further comprising drive means for continuously moving said surface at a predetermined speed, said feeding means being arranged to convey said sheets into said path at said predetermined speed and said means for producing said latent images comprising a carriage arranged to move originals with reference to said surface and means for imaging successive portions of the thus moved original onto successive portions of said surface, said carriage comprising means for actuating said timer means.

4. A combination as defined in claim 3, wherein said timer means comprises electric switch means and said means for actuating said switch means includes a projection provided on said carriage.

5. A combination as defined in claim 1, further comprising means for terminating the operation of said apparatus in response to simultaneous generation of first and second signals by said detector means and said timer means.

6. A combination as defined in claim 5, wherein said operation terminating means comprises means for terminating the movement of said surface and for deactivating said fusing means and said feeding means.

7. A combination as defined in claim 1, further comprising second timer means for generating third signals at such intervals that, during the generation of third signals, said detector means produces first signals in response to detection of successive sheets in said predetermined portion of said path in the normal course of transport of sheets along said path, andmeans for terminating the operation of said apparatus in response to the absence of simultaneous generation of first and third signals by said detector means and said second timer means.

8. A combination as defined in claim 7, wherein the meansfor terminating the operation of said apparatus in response to the absence of simultaneous generation of first and third signals by said detector means and said second timer means comprising an electric circuit.

9. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets, said fusing means comprising heat generating means; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path; timer means actuatable to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means; means for terminating the operation of said apparatus in response to simultaneous generation of first and second signals by said detector means and said timer means, said operation terminating means comprising means for terminating the movement of said surface and for deactivating said fusing means and said feeding means; and cooling means arranged to cool said fusing means irrespective of the simultaneous generation of first and second signals by said detector means and said timer means.

10. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path; said detector means comprising a signal emitting element; timer means actuatable to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheetsinto the range of said ad vancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means, said timer means comprising switch means which is actuated periodically by said means for producing said latent images; amplifier means for amplifying the first signals from said element; a logical circuit having a first input connected with said amplifier means, a second input arranged to receive second signals on closing of said switch means, and an output arranged to emit signals in response to simultaneous reception of first and second signals at said first and second inputs; and means for terminating the operation of said apparatus in response to signals from the output of said logical circuit.

11. A combination as defined in claim 10, wherein said means for terminating the operation of said apparatus comprises relay means arranged to change its condition of energization in response to signals from the output of said logical circuit and to thus immediately terminate the operation of said apparatus.

12. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path, said detector means comprising a signal emitting element; first timer means actuatable to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means; second timer means actuatable by said means for producing said latent images at such intervals that said predetermined portion of said path contains successive sheets during successive actuations of said second timer means in the course of normal transport of sheets along said path, said second timer means comprising electric switch means which is actuated periodically by said means for producing said latent images to produce third signals in response to actuation thereof; amplifier means arranged to amplify the first signals emitted by said element; a logical circuit having a first input connected with said amplifier means, a second input connected with said switch means and an output arranged to transmit signals in response to simultaneous reception of first and third signals at said first and second inputs thereof; and means for terminating the operation of said apparatus in response to signals from the output of said logical circuit.

I! II 

1. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material - which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet - by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path; and timer means actuatable by said means for producing said latent images to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means.
 2. A combination as defined in claim 1, further comprising drive means for continuously moving said surface at a predetermined speed, said feeding means being arranged to convey said sheets into said path at said predetermined speed and said advancing means comprising a pair of rotary members located at the opposite sides of said path and means for rotating at least one of said rotary members.
 3. A combination as defined in claim 1, further comprising drive means for continuously moving said surface at a predetermined speed, said feeding means being arranged to convey said sheets into said path at said predetermined speed and said means for producing said latent images comprising a carriage arranged to move originals with reference to said surface and means for imaging successive portions of the thus moved original onto successive portions of said surface, said carriage comprising means for actuating said timer means.
 4. A combination as defined in claim 3, wherein said timer means comprises electric switch means and said means for actuating said switch means includes a projection provided on said carriage.
 5. A combination as defined in claim 1, further comprising means for terminating the operation of said apparatus in response to simultaneous generation of first and second signals by said detector means and said timer means.
 6. A combination as defined in claim 5, wherein said operation terminating means comprises means for terminating the movement of said surface and for deactivating said fusing means and said feeding means.
 7. A combination as defined in claim 1, further comprising second timer means for generating third signals at such intervals that, during the generation of third signals, said detector means produces first signals in response to detection of successive sheets in said predetermined portion of said path in the normal course of transport of sheets along said path, and means for terminating the operation of said apparatus in response to the absence of simultaneous generation of first and third signals by said detector means and said second timer means.
 8. A combination as defined in claim 7, wherein the means for terminating the operation of said apparatus in response to the absence of simultaneous generation of first and third signals by said detector means and said second timer means comprising an electric circuit.
 9. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material - which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet - by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets, said fusing means comprising heat generating means; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path; timer means actuatable to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means; means for terminating the operation of said apparatus in response to simultaneous generation of first and second signals by said detector means and said timer means, said operation terminating means comprising means for terminating the movement of said surface and for deactivaTing said fusing means and said feeding means; and cooling means arranged to cool said fusing means irrespective of the simultaneous generation of first and second signals by said detector means and said timer means.
 10. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material - which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet - by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advancing means to produce first signals in response to detection of sheets in said portion of said path; said detector means comprising a signal emitting element; timer means actuatable to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means, said timer means comprising switch means which is actuated periodically by said means for producing said latent images; amplifier means for amplifying the first signals from said element; a logical circuit having a first input connected with said amplifier means, a second input arranged to receive second signals on closing of said switch means, and an output arranged to emit signals in response to simultaneous reception of first and second signals at said first and second inputs; and means for terminating the operation of said apparatus in response to signals from the output of said logical circuit.
 11. A combination as defined in claim 10, wherein said means for terminating the operation of said apparatus comprises relay means arranged to change its condition of energization in response to signals from the output of said logical circuit and to thus immediately terminate the operation of said apparatus.
 12. In an electrostatic copying apparatus, a combination comprising a driven xerographic surface; means for producing on said surface a series of electrostatic latent images by imaging successive portions of at least one original onto successive portions of said surface; means for converting said latent images into powder images; feeding means for transferring successive powder images onto successive sheets of transfer material - which are normally separated from each other by gaps each extending between the trailing edge of a preceding sheet and the leading edge of the next-following sheet - by conveying such sheets into a predetermined path wherein the leading edge of each sheet contacts said surface at a first point and the trailing edge of each sheet moves away from contact with said surface at a second point; fusing means adjacent to said path downstream of said second point and arranged to fix the powder images to the respective sheets; sheet advancing means adjacent to said path downstream of said fusing means; photoelectric detector means adjacent to a predetermined portion of said path intermediate said second point and said advanciNg means to produce first signals in response to detection of sheets in said portion of said path, said detector means comprising a signal emitting element; first timer means actuatable to produce second signals at such intervals that, while said timer means is being actuated, one of said gaps is located in said predetermined portion of said path in the normal course of transport of sheets into the range of said advancing means so that the generation of first signals by said detector means normally does not coincide with the generation of second signals by said timer means; second timer means actuatable by said means for producing said latent images at such intervals that said predetermined portion of said path contains successive sheets during successive actuations of said second timer means in the course of normal transport of sheets along said path, said second timer means comprising electric switch means which is actuated periodically by said means for producing said latent images to produce third signals in response to actuation thereof; amplifier means arranged to amplify the first signals emitted by said element; a logical circuit having a first input connected with said amplifier means, a second input connected with said switch means and an output arranged to transmit signals in response to simultaneous reception of first and third signals at said first and second inputs thereof; and means for terminating the operation of said apparatus in response to signals from the output of said logical circuit. 